THIS APPLICATION IS A U.S. NATIONAL PHASE APPLICATION OF PCT INTERNATIONAL APPLICATION PCT/JP98/03504.
The present invention relates to the field of electro-mechanical-audio converters and electro-mechanical-audio converting devices using the same employed as incoming call alerts for generating paging sounds and vibrations in mobile terminals including mobile phones, pagers, and PHSs (Personal Handy Phone SystemSets).
Mobile terminals, including mobile phones, pagers, and PHSs (Personal Handy Phone Sets) conventionally employ both an electro-mechanical-audio converting device, usually having an electro-mechanical-audio converter for its key part that generates beep sounds, and the one using the rotation of a motor that generates vibration to allow the user to select a beep or vibration to announce an incoming call. However, the use of a single electro-mechanical-audio converting device for both beep sounds and vibration is currently being proposed.
FIGS. 7 to 11 show a conventional electro-mechanical-audio converting device.
First, an electro-mechanical-audio converter, which is a key part of the device, is described. A reference numeral 1 is a housing which has an opening on its both ends. A reference numeral 2 is a movable part which has a yoke 2a mounted on the housing 1 through a suspension 3, magnet 2b, and plate 2c. A reference numeral 4 is a vibrating plate connected to a top end of voice coil 5 which includes a coil bobbin and a coil wound around the coil bobbin inserted to a magnetic gap 2d of the movable part 2. The vibrating plate 4 is also mounted on the other opening of the housing 1.
Operation of this electro-mechanical-audio converter is described next. The movable part 2 including the suspension 3 creates a mechanical resonance system by its mass and the stiffness of the suspension 3, and has its inherent resonance frequency. The vibrating plate 4 connected to the voice coil 5 also has its inherent resonance frequency by its stiffness and mass.
An electric signal applied to the voice coil 5 generates an action and reaction between the voice coil 5 and movable part 2. The electric signal matching the inherent resonance frequency of the movable part 2 strongly vibrates the movable part 2. Its vibration power is transmitted to the housing 1 through the suspension 3, and notifies the user by the feel of a vibration. When the electric signal matches the inherent resonance frequency of the vibrating plate 4 connected to the voice coil 5, the vibrating plate 4 strongly vibrates, and generates a beep sound.
As can be seen in the electric impedance frequency characteristics shown in FIG. 9, the inherent resonance frequency f01 of the movable part 2 is around 100 Hz, and the inherent resonance frequency f02 of the vibrating plate 4 is around 2 kHz. The following advantages are achieved by generating frequencies at which the movable part 2 and vibrating plate 4 respectively resonate.
More specifically, an electro-mechanical-audio device A assembled into a mobile phone 6 generates signals at a predetermined frequency to an electric signal generator 7 based on instructions given from the main body of the mobile phone 6. This electric signal is input to the electro-mechanical-audio converter A to generate sound by vibrating the vibrating plate 4. The electric signal also vibrates the movable part 2 to vibrate the main body of the mobile phone 6 so as to notify the user of the arrival of an incoming call.
If either inherent resonance frequency of the movable part 2 or vibrating plate 4 is selected as a signal of the above predetermined frequency, the movable part 2 or vibrating plate 4 resonates and generates a strong vibration or beep sound. If both resonance frequencies are selected, a strong vibration and beep sound are emitted.
The above conventional electro-mechanical-audio converter A is described with reference to both vibration and beep sound. However, some conventional electro-mechanical-audio converting devices only generate a vibration or beep sound.
As shown in FIG. 10, the largest vibration power is achieved by the resonance frequency f01 of the movable part 2 because it has the heavier mass. The resonance frequency f02 of the vibrating plate 4 may generate a loud beep sound, but its vibration power is in fact extremely small.
As described above, the electric signal generator 7 generates a resonance frequency matching a inherent resonance frequency so as to generate a loud beep sound or vibration at the electro-mechanical-audio converter A. However, the inherent resonance frequency may change due to variations in environmental conditions such as ambient temperature of the electro-mechanical-audio converter A. Or, the oscillation frequency of the electric signal generator 7 may change slightly. As shown in FIG. 9, a slight change in frequency may cause a large change in oscillation output, particularly when generating vibrations. Unstable output may result in failing to alert the user of an incoming call by vibration.
The present invention aims to provide an electro-mechanical-audio converter and an electro-mechanical-audio converting device using the same that generate a stable oscillation output.
To solve the above-mentioned problems the electro-mechanical-audio converter of the present invention includes a housing having an opening; a movable part, forming a magnetic circuit, which is mounted on the opening of the housing through a suspension; a vibrating plate mounted on the opening of the housing but away from the movable part; a voice coil whose top end is connected to the vibrating plate and a bottom part is inserted in a magnetic gap of the movable part; and a detection coil, provided near the movable part, which generates an excitation voltage by vibration of the movable part. This configuration enables the detection coil to detect strong vibrations of the movable part during resonance as the excitation voltage and feed it back. Accordingly, the present invention offers the electro-mechanical-audio converter which achieves extremely stable vibration function even when resonance frequency changes due to variations in conditions including ambient temperature.